Connecting science with society

– A chemist’s a passion to connect next-generation solar cells with “element strategy” –
  • Professor Eiichi Nakamura, Department of Chemistry

Chemistry is a field of study concerned with studying the nature, structure, and reaction of matters and creating new substances. It originated from alchemy that tried to change base metals into noble metals.

What must be undertaken today by chemists whose specialty is to handle matters? We interviewed Professor Eiichi Nakamura, Department of Chemistry, School of Science, who developed next-generation solar cell materials and was the person who proposed the national project “element strategy” which aims at a departure from dependence on rare earths.

Unveiling the shapes of molecules

A passion to see what is invisible to the naked eye was already evident in the Greek philosophy, and has definitely been a driving force for the progress of natural science. Optical microscopes invented at the end of the 16th century brought about various discoveries in biology. Electron microscopes born of the first half of the 20th century enabled us to see the more microscopic world, and they eventually led us to successfully capture the shape of angstrom (0.1 nm) sized metal atoms.

However, electron microscopes have a weakness as applied to chemistry. Organic molecules were thought to be too unstable to be observed by electron beams. To observe organic molecules intact has long been a chemists’ dream.

Figure 1

An organic molecule that changes its shape in a carbon nanotube and the molecule model (images exhibited in the 3rd Panel Exhibition of “Beauty” in Chemical Technology (2008)

Professor Eiichi Nakamura made the dream come true for the first time in the world. In 2007, he succeeded in imaging structural changes of single organic molecules in real time, together with an electron microscope researcher, Dr. Kazutomo Suenaga at the National Institute of Advanced Industrial Science and Technology. He developed a method to observe a single organic molecule placed in vacuum.

“What was surprising was that organic molecules observed were shaped just like molecular models. A molecule model is nothing but an illustration of assumed atomic nucleus positions, holistically taking into consideration the results of years of experiments by forerunners as well as the quantum chemical calculation. It entertaining that I could confirm with my eye that the real images of molecule’s structural changes and chemical reactions were similar to the motion of molecule models. I experienced myself the course of science history of the past century”, he says with a sparkle in his eyes.

Developing next-generation solar cells

Figure 2

solar cells test-produced for research (provided by Mitsubishi Chemical)

While Professor Nakamura devotes considerable effort to the basic study on molecular structures and reactivity, he also works on the research and development of “organic thin film solar cells” which is eyed as the next-generation solar cells, in collaboration with Mitsubishi Chemical Corporation.

Organic thin film solar cells broadly consist of two kinds of organic semiconductors. One is “p-type organic semiconductors” (electron donors) which emit electrons upon receiving light, and the other is “n-type organic semiconductors” (electron acceptors) which receive electrons and deliver them to electrodes. The latter, electron acceptors, use organic fullerenes developed by Professor Nakamura. A fullerene is a soccer ball-shaped molecule, composed of 60 carbon atoms. Organofullerenes are fullerenes bound with organic molecules.

“Our laboratory has developed as many as 1,000 kinds of organofullerenes in the past 20 years. They serve as great assets in putting the organic thin film solar cells into practical use”, he stresses.

Interrelation between basic and applied studies

His two kinds of research activities, the former which is a basic study and the latter an applied study appear placed at two opposite ends. He explains the relation between the two as follows.

“Observation of molecular shapes and development of solar cell materials are connected with the same purpose. The purpose of our research of synthetic organic chemistry is the production of new organic substances, and for that it is necessary to understand molecular structures and reaction mechanisms. That is why we observe real images of organic molecules. We design molecules based on theories we elucidated, estimate the functions of molecular assemblies, and incorporate the synthesized molecules into solar cells.”

He continues with the topic of relation between basic and applied studies.

“Viewed in a longer span basic studies lead to applied studies. When working on making each of the 1,000 kinds of fullerenes, you do not think about any specific applications. Study to reveal molecular structures will at some stage develop into actual applications. The boundary between basic and applied studies has to change with the times and as the research develops.”